Explain what happens during beta decay, including how the nucleus changes and what is emitted.

WJEC GCSE Physics (Wales) — 2.9 Nuclear decay and nuclear energy · Explain · 4 marks · View as Markdown

Written & reviewed by James Millett — Biology (Imperial College London), PGCE Science (University of Cambridge).

Model answer (4 marks)

During beta decay a neutron in the nucleus changes into a proton.
The mass number (nucleon number) remains unchanged.
The atomic number (proton number) increases by one.
A beta particle – a fast‑moving electron – is emitted from the nucleus.

Examiner tips

Use the phrase "neutron changes into a proton" to show the nuclear change.
State that the mass number stays the same and the atomic number increases by one.
Mention that a beta particle (electron) is emitted.
Keep the answer concise – one sentence per point.

Common mistakes

Confusing the emitted particle with a positron (beta+ decay) instead of an electron.
Saying the mass number changes instead of the atomic number.
Omitting the fact that the beta particle is an electron.

Mark scheme (4 marks)

A neutron in the nucleus changes into a proton
The mass number / nucleon number stays the same (unchanged)
The atomic number / proton number increases by 1
A beta particle (fast-moving electron) is emitted from the nucleus

Key terms in this question

beta decay